Graphene is a two-dimensional planar conducting material in which carbon atoms are bonded in a hexagonal lattice. Graphene has excellent electrical characteristics, flexibility, and high transparency and thus has been applied as a material for various electronic devices. Furthermore, since graphene has a planar structure, it has an advantage that it can be patterned by using a conventional etching method. Therefore, graphene can be easily applied to semiconductor and display device elements. However, due to a semi-metallic characteristic of graphene that has zero band gap, the application of graphene for the semiconductor device is limited. Therefore, in order to apply graphene to a channel layer of a semiconductor device, a technique that can form and control the band gap should be needed. For this, a method for synthesizing a graphene having an one-dimensional nanoribbon structure using an etching process has conventionally been studied, but there was a problem that, during the etching process, graphene is physically damaged or defects are formed, thereby degrading the electrical properties of graphene.
In order to solve the above-mentioned problem, studies about a bilayer graphene capable of forming a band gap without the etching process have been performed. Specifically the bilayer graphene has a structure where graphene is stacked up in two layers, and the band gap can be formed and controlled without damage of graphene when electric field is applied perpendicular to the bilayer graphene.
In addition, the bilayer or multilayer graphene has superior electrical conductivity and diffusion barrier characteristics compared to a monolayer graphene, and thus it is expected to be applied for interconnects of electronic devices such as semiconductor and display device elements or for a coating film of a metal surface.
Conventionally, the bilayer or multilayer graphene can be produced from graphite by a mechanical exfoliation method, but this method has disadvantages in that the yield is low and the formation of a large area film is difficult. Also, the large-area bilayer or multilayer graphene films have been synthesized so far by transferring a monolayer graphene synthesized from chemical vapor deposition repeatedly twice or more, but there were problems that production costs are high, the process time is long, an unexpected damage (e.g., tearing or wrinkling or the like) occurs during transfer process or a residual material occurs from a transfer medium, thus affecting negatively on the performance of the electronic devices. Therefore, for the commercialization of the multilayer graphene such as a bilayer or trilayer graphene, there exists a need for a technique capable of directly synthesizing the multilayer graphene to form a large area.